1. Field of the Invention
The invention pertains to synthetic textiles, and particularly to textiles made of hydrophilic polyesters.
2. Description of the Prior Art, and Other Information
The wearing hygiene and, consequently, wearing comfort of a textile depends essentially on the ability of the textile to transport heat and moisture. Natural fibers, such as cotton and wool, are hydrophilic, i.e., they absorb considerable amounts of atmospheric moisture and also exhibit a high absorbency and a high water retention capacity..sup.1 When compared with polyester fibers, natural fibers have certain drawbacks, especially when the person wearing a natural fiber textile tends to release much heat and starts to perspire. For instance, during swelling, the fiber cross section of wool increases by about 25% and that of polyester by only about 1%. Robinson, Textilpraxis International at 1180 (1976). This inhibits the permeability of the fiber to air and thus the direct transport of moisture through the meshes of the textile, especially with dense textiles. Moreover, the absorption (here absorption shall refer also to adsorption) of water by wool produces far more additional heat (113 J/g water or 27 cal/g water) than the absorption of water by polyester (3.35 J/g water or 0.8 cal/g water). Robinson, Textilveredlung at 264 ( 1977). Closely related to this heat effect is the fact that with increasing temperature the absorption capacity of wool declines distinctly..sup.2 Finally, polyester textiles dry much faster than wool textiles. The advantage of polyester in this respect is derived in particular from the fact that it absorbs much less water than wool. On the other hand, the low water absorbency (quality of having a relative tendency to absorb) of polyester is at least partly responsible for the unsatisfactory wearing hygiene and low wearing comfort of polyester fiber, together with polyester's relatively poor "feel" to the wearer, e.g., "hand". The objective of some in the art in the past five to ten years has been to try to improve this significant drawback, i.e., in particular, to increase the moisture pickup (or regain) and the water retention capacity, which are the decisive criteria of a hydrophilic behavior (cf. Robinson supra), without sacrificing favorable polyester properties..sup.3 FNT .sup.1 Hydrophilicity is the tendency of a material to exhibit a strong affinity for water, or to be readily wetted by water. FNT .sup.2 Absorption capacity is the maximum amount of moisture which a specimen may absorb under a given set of conditions. FNT .sup.3 Moisture pickup or moisture regain is the percentage of moisture in a textile material brought into equilibrium with a standard atmosphere, calculated as a percentage of the moisture-free weight.
There exists a large number of porous polyester fibers obtained by special drawing methods or by foaming with an inert gas. Like dry spun hydrophilic polyacrylonitrile fibers, the porous polyester fibers contain large pores recognizable under the light microscope which, however, do not significantly increase the moisture regain.
Porous polyester fibers with fine capillary pores not detectable under the light microscope are known to those in the art. To improve the dye rate and the relative dye uptake, H. D. Weigmann, et al., (Melliand Textilberichte at 470-473 (1976/6) have treated polyester fibers with dimethyl formamide, with subsequent treatment in boiling water to remove the solvent, followed by drying and a thermal treatment..sup.4 The Weigmann, et al., treatment led to structural changes which are essentially the result of disorientation processes in the noncrystalline regions. Depending on the temperature of the solvent treatment, a more or less pronounced secondary crystallization takes place, induced by the interaction between polymers and solvents, leading to the formation of crystallites in the swollen fiber structure. Stabilization of the swollen fiber structure prevents the total breakdown thereof when the solvent is removed, and, according to the authors, leads to the formation of voids or micropores. The properties of these traditional porous polyester products will be discussed in greater detail below, but it may be mentioned at this point that they have a comparatively low pore volume (e.g., volume of pores per unit mass of material) and consequently a low water absorption and water retention capacity. FNT .sup.4 Dye rate is that rate at which dyestuff leaves the dyebath and becomes affixed to a specimen. Dye uptake is the quantity of dyestuff, usually expressed as a percentage of the weight of a yarn or fabric, which becomes affixed to the specimen during dyeing.
It is to be emphasized that the desired pore system in Weigmann et al., is not stable, as thermal treatment above 120.degree. C. causes a drastic reduction of the relative dye uptake, and there is total collapse of the pore system at temperatures of 180.degree. to 200.degree. C. See Example 4.
In the United States, it is now well known that polyester filaments or yarns, particularly polyethylene terephthalate (PET), and that certain of these polyester fibers contain chemical additives: See U.S. Pat. Nos. 2,987,373; 3,100,675; 3,513,110 (particularly interesting because of its "open-celled structure" or significant pore space, with a pore structure of 150-5000 A, and with a density of 60-90% of the corresponding polymer, the pore structure for polyester developed by heat-treating the material at temperatures of above 100.degree. C., preferably 150.degree.-220.degree. C., and using adequate drawndown ratios, with the optional use of a defined suitable swelling agent suggested); 3,748,844; 3,953,405 (also interesting-polyesters are disclosed having 0.05-5.0 mole percent of a substituted cyclobutane dicarboxylic acid before melt polymerization; in particular PET is modified with up to 15 mole percent of a dicarboxylic acid added additionally); and 3,969,462.
Metal-containing compounds are known to stabilize polyesters against heat: see U.S. Pat. Nos. 3,475,371 (stabilizers are selected from the group of lower alkyl and lower alkenyl esters of orthosilicic acid); 3,488,318 (stabilizers containing silane complexes with alkyl and alkoxy ligands); and 3,652,493 (stabilizers containing silane complexes with aryl, hydroxy, and alkoxy ligands).
Polymers are also known to be stabilized against ultraviolet light, including oxidative decay, by the employment of metal-containing compounds, acids, and other organic substances: See U.S. Pat. Nos. 3,357,944 (oxalo-bis-hydroazide); 3,821,163 (metal complex of N,N'-alkyl esters of ethylenedinitrilo tetraacetic acid); and 3,833,542 (dichloro(di-2-pyridylamine) copper II or bis(di-2-pyridylamine) copper II chloride).
Metal-containing compounds are also known to render polymers flame-resistant or flame-retardant; U.S. Pat. Nos. 1,225,414 (Al.sub.2 O.sub.3 CO.sub.2 Na.sub.2 CO.sub.3); 3,342,898 (antimonite, borate, and silicate complexes; and 3,965,068 (combination of nickel and zinc salts).
Metal-containing compounds have also been employed to give polymers greater affinity to dye stuffs: U.S. Pat. Nos. 3,164,567 (metallosulfophenoxy-substituted benzoic or metallosulfobenzoic acid or ester); 3,166,531 (metallosulfophenoxyalkoxy-substituted aromatic monocarboxylic acid) and 3,264,255 (addition of 0.025-0.1% alkali metals).
Metal salts have also been employed as polymerization catalysts: see U.S. Pat. No. 2,850,483 (metal salt of a saturated aliphatic dicarboxylic acid containing 2-10 carbon atoms, the metal selected from Cd, Co, Mn, and Zn).
3. State of the Art
Among other approaches, attempts are now being made to improve the moisture regain properties of polyester fiber by chemical modification either of the entire polymer or of the fiber surface. So far, this has not been very successful technically or commercially, as we are advised.
Recent documented attempts in the art, many not prior art to the instant application within the meaning of 35 U.S.C. .sctn.102(b), have, inter alia, attempted to obtain hydrophilic properties for fibers by the following approaches:
(a) blending hydrophilic compounds with polyesters; PA1 (b) employing a copolymerization of acrylic compounds with polyesters; PA1 (c) irradiating polyesters; and PA1 (d) attempting a partial hydrolysis of polyesters to obtain terminal (or end) groups which are hydrophilic: --OH, --COOH, or employing alkali or sulfonate salts of polyesters. PA1 (1) M is at least one of the ions Li, Na, K, Rb, or Cs; PA1 (2) Z is one or more complex-forming central atoms from the group Mg, Ca, Sr, Ba, Zr, Hf, Ce, V, Cr, Mn, Fe, Co, Ni, Cu, Zn, Cd, B, Al, Ga, In, Sn, Pb and Sb; PA1 (3) n.apprxeq.1,.apprxeq.2,.apprxeq.3, or .apprxeq.4; and PA1 (4) m.apprxeq.2,.apprxeq.3, or .apprxeq.4, where .apprxeq. means "about"
See V. N. Sharma, "Hydrophilicity of Textile Fibers and Its Influence on Fabric Wear Properties", COLOURAGE at 23-27 (May 11, 1978) for a good summary of the state of the art.
Patent publications evidencing the state of the art are (1) German Offenlegungsschrifts 2,719,019 (published Nov. 2, 1978); 2,554,124; 2,637,394; 2,757,787; 2,724,952; 2,713,456; 2,709,403; 2,706,522; 2,706,032; 2,705,210; 2,703,372; 2,207,503; 2,703,051; 2,659,616; 2,659,263; 2,657,144; 2,642,195; 2,633,838; 2,627,708; 2,625,908; 2,611,193; 2,610,626; 2,609,829; 2,607,996; 2,607,659; 2,607,071; 2,044,281 (see U.S. Pat. Nos. 3,695,992; 3,792,019; and 3,760,054); and 2,605,412; (2) Japanese Patent Publications 74,014,878; 74,729,485-Q; 74,030,711; 51,055,367; 50,107,290; 52,081,130; 52,074,020; 52,085,582; 52,096,297; 48,084,853; 48,019,093; 49,100,395; 7,203,850-R; 48,075,894; 48,093,665; 49,030,694; 49,066,991; 75,039,759; 7,317,204-R; 4,856,999-Q; 7,001,679-R; 75,012,007; 49,108,395; and 7,308,270; (3) U.S. Pat. Nos. 4,043,985; 4,101,525; 4,134,882; 4,070,342; 4,000,109; and 4,116,931; and (4) Swiss Patent Publication 468,213;
See also the following publications, summarizing the state of the art: first, pertaining to the recent Bekleidungsphysiologisches Institut E. V. (Sept. 27-28, 1978) at 7124 Boenigheim (Schloss Hohenstein), West Germany: (1) Hans Seghezzi, "Bekleidungsphysiologische Erkenntinisse rucken im Spiel um Markt und Verbrauchergunst immer mehr in den Vordergrund", Wirkerei- und Strickerei-Technik, Bamberg, No. 12 at 705-708 (Dec. 1978) and (2) K. H. Umbach, "Bekleidungsphysiologie heute", Chemiefasern/Textilindustrie at 42-47 (January 1979); second, other recent art (not prior art within .sctn..sctn.102(b)-103 unless published before Dec. 12, 1976): Peter Hoffmann, "A New Generation of Synthetic Fibers-Moisture-Absorbent Bayer Textile Fiber", Teintex No. 4 at 174-186 (1977); "Neue Bayer-Entwicklung: Saugfahige Acrylfasern als neue Synthesefaser-Generation", Chemiefasern/Textil-Industrie at 1045-1046 (December 1976); Rene Penisson, "Wege zur Modifizierung von Chemiefasern", Lenzinger Berichte 36 at 24-34 (February 1974); Rolf Kleber, "Moglichkeiten zur Oberflachenmodifizierung synthetischer Fasern in der Textilausrustung", Lenzinger Berichte 33 at 64-71 (December 1972); M. Preitscher and T. Robinson, "Hydrophiles Ausrusten von Synthesefasern und deren Mischungen mit Cellulosefasern:Problematik und Prumethoden", Textil Praxis International at 1180-1190 (October 1976); "Hydrophiles Ausrusten von Synthesefasern und deren Mischungen", Textilveredlung at 264-268 (1977); C. I. Simoneseu, et al., "Die Pfropfung von Polyathylenterephthalat unter elektrischen Entladungen bei hohen Frequenzen", Rev. Roum. Chim. 22 (6) at 911-921 (1977); J. J. Choi, C. K. Lee, and K. J. Lee, "Radiation grafting of Hydrophilic Monomers onto Polyester", J. Korean Nucl. Soc. 5 (2) at 103-114 (1973); G. Gaussens and F. Lemaire, "Semiindustrial Production and Properties of Radiochemically Treated Hydrophilized Synthetic Textiles", Rev. Gen. Caout. Plast. 50 (11) at 911-915 (1973); G. Gaussens and F. Lemaire, "Hydrophilic Polyamide and Polyester Textiles by Grafting", Inf. Chim. 119 at 207-210 (1973); D. Zyska, A. Michaltska, "Studien der hydrophilen Behandlung von Synthesefasergeweben", Prace Inst. Wlok. 16 at 201-208 (1966); T. Okada, "Strahlungsinduzierte Modifizierung von Fasern", C. A. 70 (22) at 97823b (1969); K. Okada, "Strahlungs-Pfropfpolymerisation von hydrophilen Monomeren auf Polyesterfasern", C. A. 72 (18) at 91366 (1970); "Saugfahige Textilfaser:Eine neue Generation der Synthesefasern", Wirkerei-und Strickerei-Technik, Coburg, No. 9 at 442-445 (September 1977); F. Gelejietal, "Modifizierung der elektrostatischen Aufladung, der Anfarbbarkeit und der mechanischen Eigenschaften von Synthesefasern durch Pfropfen", Lenzinger Berichte 33 at 199-207 (December 1972); Charles Sarmany et al., "Eine neue hydrophile Polamidfaser", Lenzinger Berichte 44 at 85-89 (1978); J. Hoigne et al, "Strahlungschemische und radikalische Modifikation synthetischer Fasern", Textilveredlung 5 (5) at 400-406 (1970); M. Preitscher et al, "Hydrophiles Ausrusten von Synthesefasern und deren Mischungen mit Cellulosefasern-Problematik und Prumethoden", Textil Praxis International at 1180-1190 (October, 1976); T. Robinson, "Hydrophiles Ausrusten von Synthesefasern und deren Mischungen", Textilveredlung 12 (6) at 264-268 (1977); R. Teichmann, "Durch Pfropfpolymerization realisierbare Eigenschaftsverbesserungen an textilen Substraten:Eine Literaturubersicht", Faserforschung und Textiltechnik 26 (2) at 66-88 (1975); V. Hochman, " Die Anwendung licht-und elektronenmikroskopischer Methoden zur Untersuchung der Morphologie synthetischer Fasern", Faserforschung und Textiltechnik 27 at 417-424 (1976); W. O. Statten, "Polymer Texture: The Arrangement of Crystallites", J. of Polymer Science 16 at 143-155 (1959); W. O. Statten, "Crystallite Regularity and Void Content in Cellulose Fibers As Shown by Small-Angle X-Ray Scattering", J. of Polymer Science 22 at 385-397 (1956); W. O. Statten, "Microvoids in Fibers as Studied by Small-Angle Scattering of X-Rays", J. of Polymer Science 58 at 205-220 (1962); H. Domimetsch, "Zur Ausbildung der Faserstruktur beim Strecken von Polyathylenterephtalatfilamenten", Chemiefasern/Textilindustrie at 1086-1092 (December 1976); Hans-Dietrich Weigmann, et al., "Die thermische Stabilitat von losungsmittel-induzierten Strukturanderungen in Polyesterfasern", Melliand Textilberichte at 470-473 (6/1976); M. Sutton, et al., "Resultats Relatifs a l'etude des Structures Poreuses des Fibres Textiles en Microcopies Optique et Electronique", Bull. Sci. Inst. Textiles France 24 at 763-781 (1970); H. D. Weigmann, et al., "Interactions of Non-aqueous Solvents with Textile Fibers; Part IV-Effects of Solvents on the Mechanical Properties of Various Textile Yarns", Textile Research Institute at 165-173 (March 1974); B. H. Knox, et al., "Interactions of Nonaqueous Solvents with Textile Fibers; Part V-Application of the Solubility Parameter Concept to Polyester Fiber-Solvent Interactions", Textile Research Institute at 203-217 (March 1975); H. D. Weigmann, et al., "Fiber Solvent Interactions and Dyeing Behavior-Progress Report No. 27-Aug. 1, 1976, to Nov. 30, 1976", Textile Research Institute, Princeton, N.J. (1977); H. D. Weigmann, et al., "Fiber Solvent Interactions and Dyeing Behavior-Progress Report No. 26-Apr. 1, 1976 to July 31, 1976", Textile Research Institute, Princeton, N.J. (1976); A. S. Ribnick, et al., "Interactions of Nonaqueous Solvents with Textile Fibers-Part II-Isothermal Skrinkage Kinetics of a Polyester Yarn", Textile Research Institute Journal 43 at 176-183 (March 1973); A. S. Ribnick, et al., "Interactions of Nonaqueous Solvents with Textile Fibers-Part III-The Dynamic Shrinkage of Polyester Yarns In Organic Solvents", Textile Research Journal 43 at 316-325 (June 1973); L. Rebenfeld, "Das Verhalten von Textilfasern unter Einfluss chemischer Behandlungen", Lenzinger Berichte 40 at 22-29 (1976); H. D. Weigmann, et al., "Interactions of Nonaqueous Solvents with Textile Fibers; Part VII-Dyeability of Polyester Yarns After Heat and Solvent-Induced Structural Modifications", Textile Research Journal 46 (8) at 574-587 (1976); H.D. Weigmann, et al., "Pulse Propagation in Polyester-Solvent Systems", J. of Applied Science 20 at 2321-2327 (1976); "Bayer-Textilfaser-Eine neue Generation Acrylfaser tritt an", Textil-Wirtschaft at 25 (Nov. 25, 1976); "Bayer A. G.-Absorptive Fiber for a Feeling of Comfort-Sensationelle Neuentwicklung auf Acryl-Basis", Textil-Mittelungen 31 (141) at page 1 (Nov. 23, 1976); "Eine neue Faser von Bayer", Frankfurter Allgemeine Zeitung at 7 (No. 264, Nov. 23, 1976); and "Neue saugfahige Acrylfaser", Melliand Textilberichte at 11-12 (January 1977).
In the process of Toray, British Patent Specification No. 1,285,584 (corresponding to U.S. Pat. No. 3,682,846), the hydrophilic properties are obtained by the addition of 0.4-5 wt. percent polyalkylene ether and 0.3-3 wt. percent of a surfactant metal salt to the polyester resin. The metal salts disclosed in the patent are salts of carboxylic acids, phosphonic acids, or sulfinic acids. At any rate, salts of phosphonic and sulfinic acids can be disregarded; they are not related with the oxalato complexes to be used according to the instant invention, which are described in great detail, infra. There is little similarity between the carboxylic acid salts of British Patent Specification 1,285,584 and the oxalic complexes used in the instant invention. The carboxylic acid salts used in the Toray process must have surfactant properties and have at least one hydrophobic group, e.g., an alkyl group, in the molecule. Consequently, long chain fatty acid salts, e.g., sodium, potassium or zinc salts of caproic, stearic, pelargonic and nonadecylic acid are used. Most importantly, Toray teaches only simple carboxylic acid salts. By contrast, the additives of the instant invention are oxalato complexes, not possessing any surfactant properties, and do not contain alkyl residues. Simple oxalate salts were proved to be ineffective in the instant invention (see Example 1, infra).
Second, the metal salts in British Patent Specification 1,258,584 are used in combination with polyalkylene ether. As sole additives, they are ostensibly ineffective. By contrast, the process of the instant invention, aside from the added oxalato complexes, requires no further additives.
Third, Toray products allegedly have pores of 0.01-3 micron diameter. This range coincides only partly with the pore size range of the hydrophilic polyester according to the instant invention, which has many pores less than 0.03 micron (300 A). See FIG. 8 herein.
Fourth, the Toray products are said to have a pore volume of 0.5-10 percent, which is considerably less than the pore volume of hydrophilic polyesters according to the instant invention, which is at least about 30 percent of the total volume of the fiber. Additionally, the Toray patent specification does not indicate that the Toray products exhibit capillary condensation. The Toray products do not have measurable capillary condensation and have moisture regain of less than about two percent. In contrast to the products of Toray, the products according to the instant invention have a surface wettability (drop test) comparable to that of unmodified polyester. The Toray product, on the other hand, has a substantially higher surface wettability. In contrast to the Toray products, the products according to the instant invention have no antistatic properties. Finally, based on some indications in the Toray applications, the presence of pores having a diameter of less than 0.03 micron in the Toray product is doubtful.
Prior to the instant invention, the best attempts to obtain a hydrophilic polyester having the desired effects were obtained by physical modification of the fiber structure, e.g., by increasing the fiber surface capable of absorption. Melliand Textilberichte at 11-12 (January 1977) describes the structure principle of such a fiber, which has apparently already been realized for polyacrylonitrile fibers. Said polyacrylonitrile fibers consist of a core comprising a large number of fine capillary pores and a dense skin having a plurality of fine channels able to transport water laterally into the porous fiber core. The purpose of the skin is to protect the inner pore system and insure trouble-free processing.
German Offenlegungschrift 25,54,124 (published June 8, 1977, and not prior art under 35 U.S.C. .sctn.102(b) to the instant application) describes a process for obtaining hydrophilic polyacrylonitrile fibers by a dry spinning process, whereby 5 to 50 weight percent of a hydrophilic compound liquid (based on the total weight of the solution) is employed having a higher boiling point than the spinning solvent used, (1) being readily miscible with the spinning solvent and with water and (2) constituting a nonsolvent for the polymer to be spun. This compound is added to a suitable spinning solvent, such as dimethyl acetamide, dimethyl sulfoxide, N-methylpyrrolidone or dimethyl formamide. Cited examples of said liquids are: alkyl ethers and esters of high boiling alcohols, esters, and ketones; preferably use is made of glycerine. The resulting filaments have a skin/core structure, a porous core with average pore diameters of 500 to 1000 nm (=5000 to 10,000 A), a moisture regain of about 2 to 5 percent (at 65 percent relative humidity and 21.degree. C.) and a water retention capacity of 10 to 30 percent.
Fibers of a skin/core structure dry-spun from acrylonitrile polymers with a moisture regain of at least 7 percent (at 65 percent RH and 21.degree. C.) and a water retention capacity of at least 25 percent are described in German Offlegungschrift 26,07,071 (published Aug. 25, 1977, not prior art under 35 U.S.C. .sctn.102(b) to the instant application). These fibers are obtained by spinning an acrylonitrile polymer containing carboxyl groups from a solvent to which has been added 5 to 50 weight percent (referred to the total weight of the solution) of a compound whose boiling point is higher than that of the spinning solvent. Furthermore, the compound is miscible with water and the spinning solvent and does not dissolve the copolymer. The freshly spun yarn is washed to remove the compound added to the solvent and converting all or part of the carboxyl groups to the salt form.
This process of modifying polyacrylonitrile to improve hydrophilic properties is not technologically suitable to improve the hydrophilic properties of polyesters, since, on a production basis, polyesters are melt spun at close to 300.degree. C. Polyester is spun under much more critical conditions than polyacrylonitrile, which is dry spun from organic solvents at comparatively low temperatures. Moreover, unmodified polyacrylonitrile already has a comparatively high moisture regain of about 1.5 percent. Unmodified polyester on the other hand has a much lower moisture regain of only about 0.3 to about 0.6 percent.